The present embodiment relates generally to a cementing composition for sealing a subterranean zone penetrated by a well bore.
In the drilling and completion of an oil or gas well, a cementing composition is often introduced in the well bore for cementing pipe string or casing. In this process, known as “primary cementing,” the cementing composition is pumped into the annular space between the walls of the well bore and the casing. The cementing composition sets in the annular space, supporting and positioning the casing, and forming a substantially impermeable barrier, or cement sheath, which isolates the well bore into subterranean zones. Thus, the undesirable migration of fluids between zones is prevented after primary cementing.
Changes in pressure or temperature in the well bore over the life of the well can result in compromised zonal isolation. Also, activities undertaken in the well bore, such as pressure testing, well completion operations, hydraulic fracturing, and hydrocarbon production can affect zonal isolation. Such compromised zonal isolation is often evident as cracking or plastic deformation in the cementing composition, or de-bonding between the cementing composition and either the well bore or the casing.
As the name implies, cementing compositions are made chiefly of cement. Due to its incompressible nature, neat cement is undesirable for use where there is a chance of expansion or contraction in the well bore. Cement has a high Young's modulus, and fractures at slight strains when subjected to stresses (“brittle failure”). When the imposed stresses exceed the stress at which the cement fails, the cement sheath can no longer provide zonal isolation. While the Young's modulus of cementing compositions can be lowered by adding silica compositions, such silica treated cementing compositions (“water-extended slurries”) suffer from lower compressive and tensile strengths.
Therefore, a cementing composition that can provide greater elasticity and compressibility, while retaining high compressive and tensile strengths, is desirable for primary cementing.